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A curved switching surface (SS) for inverters control with superior characteristics is geometrically derived in this paper. In order to avoid inaccuracies introduced by simplification or assumptions, the analysis is performed entirely using a versatile geometrical method in the normalized domain. Unlike previous approaches, both the output voltage and the capacitor current are considered as varying references to establish a more accurate control law with enhanced performance. The proposed normalization technique provides remarkable insight into the behavior of system, the leading to a pure geometrical treatment that is general and applicable to any possible inverter. As a result of a rigorous analysis, a control law for inverters defined as natural SS is proposed and thoroughly characterized. In addition to the enhanced dynamic response, fixed-frequency operation is one of the key features of the proposed control scheme. In order to formally demonstrate fixed-frequency operation, a transformation from the natural SS to its pulsewidth modulation (PWM) equivalent is performed, revealing duality between boundary control using curved SS and traditional PWM. This is a significant advancement toward the unification and understanding of traditional modulation against modulation produced by curved SSs. Finally, an additional novel concept is explored: operation in mixed monopolar and bipolar mode using the natural SS. This new mixed operating mode overcomes physical limitations of the inverter structure in monopolar mode around the region of zero voltage cross (both the problem identification and solution are investigated). Experimental results of a 1.5-kVA inverter operating at fixed moderate frequency are presented to validate the natural SS performance, illustrate the benefits of the normalization technique, and demonstrate the monopolar and mixed operating mode. Index Terms--Boundary control, curved, inverter, nonlinear control, switching surface.

A general procedure for the selection of a curved switching surface (SS) to control buck-type converters is presented in this letter. The analysis is based on the normalized representation of ideal SSs for different loading conditions. The normalization process leads to a unique representation of the SSs for any possible buck converter. A set of graphics in three dimensions is introduced to give a spatial sense of the behavior of the converter and its control requirements during transients. As a result of the investigation, a switching surface referred to in this letter as the natural unloaded SS is selected, providing excellent transient behavior and no overshoot during startup. For any buck converter with typical parameters, this control scheme produces, in one switching action, a minimum of 99% of the desired output voltage. The general concept of using second-order SS is also geometrically analyzed in this letter to clarify its characteristic features and disadvantages. Experimental results for a typical buck converter are presented to illustrate the transient behavior of the converter during startup and sudden load changes. The results confirm the virtues of the control scheme. Index Terms--Normalized switching surface (SS), buck converter, large-signal transient response.

Three-phase CLLC resonant converters provide higher power conversion capability as compared to half-bridge and full-bridge structures. In addition to the unique features of CLLC converters for bidirectional applications, the three-phase structure provides significantly reduced output current ripple (smaller output capacitor), parallel power processing (reduced components size and current peak stress), and better thermal distribution (smaller heatsinks). However, with practical, i.e., nonzero, resonant component tolerances, these benefits are normally less, and sometimes significantly less than expected in the ideal case. In this article, the unbalanced behavior of the converter with 15 unknown resonant components is identified and analyzed. A new analysis methodology is proposed to investigate the worst-cases of current-sharing among above 32 000 possible scenarios in three-phase CLLC resonant converters. In addition, this article shows that phase-shifting techniques can be effective to mitigate the unbalanced behavior of the converter. The proposed analysis in this article helps to determine the highest admissible tolerance in the components to keep the converter working within a certain range of unbalanced behavior without requiring any balancing techniques. The proposed analytical framework is verified with experimental and simulation results of a 3-kW bidirectional three-phase CLLC experimental prototype. [ABSTRACT FROM AUTHOR]

Charge control for resonant converters introduces an inner feedback loop that improves the system dynamic characteristics. However, small-signal modeling is not as straightforward with charge-controlled resonant converters as it is with current mode hard-switching topologies, due to the nature of resonant behavior. Conventional small-signal models for charge-controlled resonant converters are developed based on the converter input and output energy balance. This simplified approach overlooks the dynamics of the magnetizing inductor current and generates errors in small-signal frequency response. To improve the analytical model and enable high-bandwidth design, this article proposes a new methodology for modeling charge-controlled resonant converters. The energy stored in the resonant tank is analyzed using the theory of extended describing function, which accounts for the effect of the magnetizing current. This methodology applies to a wide range of charge control variants, such as bang-bang charge control and hybrid-hysteretic control. To demonstrate the modeling procedure, this article considers a high-order, five resonant-component half-bridge CLLC resonant converter as a case study. The proposed analytical model is applied to a 1 kW, 400-V/3.3-A power supply prototype for simulation and experimental validation. The proposed model successfully predicts the frequency response of the resonant converter across frequency and load conditions, providing rapid frequency-domain evaluation in the design process. [ABSTRACT FROM AUTHOR]